This invention relates to a cylinder insert structure used in an internal combustion engine such as an automotive engine.
An internal combustion engine has an engine block with a number of cylinder openings therein. The pistons of the engine move within the cylinder openings in a reciprocating fashion. The pistons are driven downwardly by the appropriately timed combustion of a mixture of fuel and air in a combustion space between the top of each piston and the bottom of a cylinder head.
Some types of engine blocks are cast from aluminum-base alloys. The use of aluminum-base alloys rather than iron-base alloys reduces the weight of the engine because of the lower density of the aluminum-base alloys. The reduced weight improves the gas mileage of the vehicle.
The aluminum-base alloys work well for most of the engine block. However, they do not have sufficiently good strength and wear resistance at elevated temperatures to serve as the interior liner of the cylinder against which the piston slides and against which there is the combustion of the mixture of fuel and air. Several techniques have been used to improve the properties of the portion of the engine block that defines the cylinder openings. In one, that portion of the aluminum-base alloy is strengthened and/or hardened, as by the addition of alloying elements, coatings, or composite reinforcement.
In another approach that has generally gained the greatest acceptance, a cylinder liner of an iron-base alloy (e.g., steel or cast iron) is provided. A water jacket overlies the exterior of at least a part of the iron-base cylinder liner. To manufacture a cylinder block using an iron-base cylinder liner, the aluminum-base alloy is cast around iron-base cylinder liners already prepositioned within a mold.
This approach works well for many conventional uses of such engines. However, in other applications, such as a high-performance racing engine based on a modified stock engine block, the present inventor has observed that there are engine failures associated with the cylinder liner. There is a need for an approach to overcome these failures, while retaining the other advantageous features of the standard engine. The present invention fulfills this need, and further provides related advantages.
This invention provides an internal combustion engine with a cylinder insert that is not prone to failure in demanding applications. The cylinder insert is readily manufactured and is suited for use both in new construction and in the modification of conventional stock engines. It is compatible with the structure of conventional stock engine blocks, so that only minimal modifications of the conventional stock engine blocks are required to utilize the present cylinder insert. An engine with the engine block modified to use the present cylinder insert may be pushed to performance levels well in excess of those of conventional engine blocks without failures.
In accordance with the invention, an internal combustion engine includes an engine block having a head seat surface and a cylinder opening extending from the head seat surface into an interior of the engine block, and a cylinder insert residing within the cylinder opening and having an insert upper surface substantially flush with the head seat surface of the engine block. The cylinder insert has a smooth cylindrical inner surface with a longitudinally extending cylindrical axis, and a stepped outer surface formed of three longitudinal regions. The three longitudinal regions include a first longitudinal region adjacent to the insert upper surface and having a first wall thickness, a second longitudinal region remote from the first longitudinal region and having a second wall thickness less than the first wall thickness, and a third longitudinal region intermediate between and continuous with the first longitudinal region and the second longitudinal region. The third longitudinal region has a third wall thickness intermediate between the first wall thickness and the second wall thickness. Typically, there are at least two cylinder openings, and there is a cylinder insert as described above for each of the cylinder openings.
In an embodiment of most interest because it is well suited to the modification of an existing stock engine, an internal combustion engine includes an engine block having a head seat surface and a cylinder opening extending from the head scat surface into an interior of the engine block. The cylinder opening has a cylinder opening surface, and a cylinder opening cylindrical wall that is cylindrical about a longitudinally extending cylindrical axis and has a wall upper surface located at a recess depth below the head seat surface. The cylinder opening wall has a cylinder opening inner cylindrical diameter and a cylinder opening outer dimension such that there is a gap between the cylinder opening cylindrical wall and the cylinder opening surface. A cylinder insert resides within the cylinder opening and has an insert upper surface substantially flush with the head seat surface of the engine block. The cylinder insert comprises a smooth cylindrical inner surface that is cylindrical about the longitudinally extending cylindrical axis, and a stepped outer surface formed of three longitudinal regions. The outer surface includes a first longitudinal region adjacent to the insert upper surface and having a first wall thickness such that the first longitudinal region contacts the cylinder opening surface, and a second longitudinal region remote from the first longitudinal region and having a second wall thickness less than the first wall thickness, the second longitudinal region being received within the cylinder opening inner wall. There is a third longitudinal region intermediate between and continuous with the first longitudinal region and the second longitudinal region, the third longitudinal region having a third wall thickness intermediate between the first wall thickness and the second wall thickness. A support shoulder lies between the second longitudinal region and the third longitudinal region and rests upon the wall upper surface.
Desirably, the cylinder insert contacts the engine block in the first longitudinal region and the second longitudinal region, but does not contact the engine block in the third longitudinal region so that the gap is continued into this volume. Cooling water is circulated in the gap between the cylinder insert and the engine block.
The engine block preferably comprises an aluminum-base alloy and the cylinder insert preferably comprises an iron-base alloy such as a cast iron.
The cylinder insert of the invention has its thickest wall in the first region near the top of the cylinder opening. The greatest wall stresses in the cylinder insert are produced in this first region by the combustion of the mixture of fuel and air, requiring the greatest wall thickness. The first region need not have a great longitudinal length, because the magnitude of the combustion-induced stresses falls rapidly with increasing distance from the top of the cylinder and the insert top. The wall thickness of the cylinder insert is therefore reduced by reducing the outside diameter of the cylinder insert a short distance from the insert top. This reduction in the wall thickness of the cylinder insert provides both a shoulder for supporting the cylinder insert in the engine block and also decreases the thermal impedance to heat flow out of the insert wall and into the surrounding water jacket.
The invention is described herein as applied to one of the cylinders of an internal combustion engine. More commonly, the internal combustion engine has multiple cylinders, and a cylinder insert as described herein is provided for each of the cylinders.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.